The present invention is directed to printed wiring boards having recesses, or other non-conductive surfaces, made electrically conductive by applying a coating containing carbon, preferably graphite, to an initially nonconductive through hole or other surface.
The prior art, for example U.S. Pat. No. 3,224,986, discloses water-insoluble, water-insensitive polymers made by (1) forming a polyamide, (2) reacting the polyamide with epichlorohydrin to make a cationic, water-soluble, thermosetting resin; and (3) reacting the resin with a water-soluble polymer, such as carboxymethylcellulose or others, in water at a low pH. Related disclosure may be found in U.S. Pat. Nos. 3,658,873; 3,049,469; 3,962,159; 3,917,894; 4,037,017; 4,152,199; 2,926,116; 2,926,154; 3,332,834; 3,592,731; and 3,763,060. All the patents listed in this paragraph are hereby incorporated by reference. These patents assert that various polysaccharides, such as starches and carboxymethylcellulose, react with polyamide-epichlorohydrin resins to form water-resistant coatings.
Additional background information about conductive coatings for through holes may be found in U.S. Pat. No. 5,690,805. That patent is hereby incorporated by reference in the present disclosure.